1. Field of the Invention
The present invention generally relates to a power controlling method, and more particularly, to a device for performing an uplink power control operation in a mobile communication system and a method thereof.
2. Description of the Related Art
In a radio channel used in a mobile communication system, attenuation of a propagation path greatly varies according to distance and shadowing, and a Carrier to Noise and Interference (C/I) ratio greatly varies according to a channel state since the radio channel has large inter-cell interference and fading. In an Orthogonal Frequency Division Multiplexing Access (OFDMA)-based packet communication system, since a cell uses a subcarrier having a same index as that of a subcarrier of another cell, an Other-Cell Interference (OCI) occurs. Accordingly, the magnitude of Noise and Interference (NI) to a Subscriber Station (SS) varies according to an amount of OCIs.
In an OFDMA system, since power of a subscriber station in another cell acts as the OCI and the amount of interference that continuously varies greatly affects throughput of the entire system, it is important to control the power of the subscriber station to minimize the interference. Accordingly, an uplink power control operation considering the interference received from a neighboring cell is performed.
The uplink power control operation is performed while considering an average value of the NIs caused in a previous frame of each cell, an average Carrier to Noise and Interference ratio (C/N) value, and a user path attenuation value. Generally, a closed-loop power control operation or an open-loop power control operation is performed for the uplink power control operation, which is usually performed for one cell. Path attenuation, channel characteristic variation, channel estimation error, and power control delay time are compensated for the interference and signal of the subscriber stations in one base station.
In the open-loop power control operation, the NIs to the subscribe station in all slots of one downlink frame are estimated, an average value of the estimated NIs are calculated for each cell, and a current average NI is estimated for each cell. The estimated current average NI is transmitted to each subscriber station of a corresponding cell. Each subscriber station uses the transmitted average NI to calculate the CN value, estimates its own path loss value, and applies the respective values to an equation for the open-loop power control to determine the power to be used in a subsequent frame. Subsequently, the subscriber station transmits a signal according to the power determined in the subsequent frame. The above process is repeatedly performed for each frame to perform the power control operation.
The average NI generated in a previous frame of the frame transmitting the signal is used to determine the power. Since the average NI of the previous frame varies according to packet generation and a hitting state of the subsequent frame, the power control based on the average NI of the previous frame is inaccurate.
In another power control method according to time, the power control is performed in each frame for each subscriber station. For example, the average NI of a (i+3)th frame is estimated, and the estimated NI is used to perform the open-loop power control at a starting point of a subsequent (i+4)th frame.
However, in the OFMDA system, the NI continuously varies as traffic of packets transmitted for each frame increases or decreases. Accordingly, a substantial error may occur between the NI estimated in the current frame and an actual NI generated in the subsequent frame.
Accordingly, as described above, since the average NI of the current frame is used to determine the power of the subsequent frame when the NI for the power control is estimated, an inaccurate NI is used, and a power control error may occur.
The above information is only for enhancement of understanding of the background of the invention and may contain information that does not form prior art that is already known in this country to a person of ordinary skill in the art.